The present invention relates to a single panel type liquid crystal display (LCD) projector, and more particularly, to a single panel liquid crystal display projector which can satisfy the focus characteristic by inserting a mirror in the optical axis of an optical system and miniaturize the size of the apparatus.
In general, an LCD projector is a system which obtains a synthetic screen after screening each color generated from red, green and blue LCDs by means of a dichromatic mirror. Such a system was originated from a projection television system.
A projection television system obtains a final pixel on a large screen provided separately by radiating three specific cathode ray tubes having three primary colors of light; red, green and blue, transmitting and enlarging the pixel by using a magnifying lens and a reflecting mirror.
However, along with the development of semiconductor integrating technology and precision processing technology, recently, a method of driving each pixel by a specific driving apparatus has achieved high-quality and high-minuteness of the LCD panel by installing an RGB filter on a single LCD panel. Therefore, only projecting the light transmitted by irradiating parallel light from the rear side of the LCD panel by means of a projecting lens enables sufficiently high quality to be obtained.
In FIG. 1, an internal optical system is schematically shown in the conventional flat panel type LCD projector.
Referring to FIG. 1, there are installed a focusing lens system 11 composed of multiple convex and concave lenses, a condensing lens 12, an LCD panel 13 and a light source lamp 14, which are aligned on a common optical axis. In such an arrangement, unless the magnifying ratio of the condensing lens 12 is considerably large, the distance between the condensing lens 12 and the focusing lens system 11 cannot be reduced. In other words, the light irradiated from the light source lamp 14 is reflected by the concave hemispheric reflecting mirror 15 or directly irradiates the LCD panel 13 intensively. At this time, to place the image of the light source lamp 14 on the iris of the focusing lens system 11, the condensing lens 12 should have a predetermined magnification. Here, the condensing lens 12 is used for focusing as well as condensing. In order to reduce the distance between the focusing lens system 11 and the condensing lens 12 for the purpose of decreasing the size of the apparatus, the magnification of the condensing lens 12 should be considerably increased, as described above. This means that the lens should be thick. If the lens becomes thick, the spherical aberration is increased correspondingly, thereby making it difficult to correct the overall optical system. Also, as the thickness of the lens is increased, the chromatic aberration is increased, accordingly.
Meanwhile, FIG. 2 schematically shows a usage example of the conventional flat panel type LCD projector.
Referring to FIG. 2, since the projector 20 is movable, the optical axis is located in the center of the projector 20 and the projector 20 is mainly used in the state of placing on a table 30, an upward projection is necessary, compared to the optical axis of the lens, as shown. In such an instance, the optical axis of the lighting system is placed lower than the optical axis of the lens. That is to say, the optical axis gap of .increment.y is produced, as shown in FIG. 1. In this connection, if the optical axis and the screen 40 are not perpendicular, a trapezoid distortion is generated on the screen 40. Therefore, as shown in FIG. 1, the LCD panel 13 is installed lower than the optical axis for an upward projection. However, in this case, since the lens should be designed for a broader image angle, the burden in manufacturing the lens becomes higher.